LDS vs The Burst Disk

[JackD342]

Lately, DIN valves seem to almost always seem to come with 5250 psi burst disks by default. Which are technically "too high" for 3000psi tanks. If your shop wants to put in a 5000psi disk then they are correct and the easiest thing is to just let them do it. Practically speaking, the 250psi difference is irrelevant.

Your 5250 disks aren't a property of DIN valves, they are a property of valves sold for use with 3442 steel cylinders with the Exemption permits. Usually the burst disk installed is the only difference between valves rated for different pressures - there are NOT different valve designs for each different cylinder pressure.
Here is the XS Scuba parts list for burst discs, which you will see aligns with the information already posted by @runsongas (once you round 3442 up to 3500, that is)

I agree, 4250 sounds like it is probably not the actual marking on the disk assembly.

And these ratings and pressures are not intended to be applied "at least" or "at most" the rated pressure. They are to be used at the actual rated pressure, neither too high nor too low.

 

[rjack321]

Your 5250 disks aren't a property of DIN valves, they are a property of valves sold for use with 3442 steel cylinders with the Exemption permits.

Technically yes, in practically I have bought a whole ton of valves lately as I was sick and tired of trying to pick out and replace crush washers in my old thermos. They have been coming with 5250 disks by default nowadays. For 2400 and 3000psi tanks I just use them. For my single 2015psi service pressure tank and my 2250psi tanks I swap them out.

 

[Tribal]

You guys are funny. Psi, feet, Fahrenheit, burst discs, ...

Why do it the easy way if you can do it the hard way .

 

[viperwsu]

Without adversity, how can you appreciate victory?

 

[2airishuman]

I bought a new valve/reg from Piranha, and it has a burst disk in it with the simple marking of "4250".

The LDS has it right now because I brought in my pony for hydro last week - last night while I was there for something else, the owner pulled me in the back because of an "issue" with the valve. He pulled out a tupperware box filled with the parts of my brand new, USPS-delivered-20-min-before-I-dropped-it-off, valve - which I specifically said was brand new and not be screwed with. I even gave them the receipt from Piranha to prove it was new.

The issue, LDS says, is that the burst disk is for 4250PSI rated tanks and isn't safe on a 3000PSI tank.
Randy from Piranha assured me that that number is the burst pressure, not the service pressure. Since I've never heard of a dive tank rated to that high of a pressure I'm inclined to believe Randy. LDS is emphatic that the disk is dangerous, and says it needs to be replaced before the valve can be used despite the shop owner having spoken with Randy personally.

Has anybody else seen burst discs marked with nothing but the burst pressure, and not the tank service pressure? My research shows me a variety of markings, but nothing that's just the burst pressure. I'd love to be able to show some evidence to the LDS even though I'm going to go rescue my valve before they start taking off more parts or otherwise screwing with it.

1) You mean 5250, not 4250.
2) Yes, that is the burst pressure, and that is the way the one-piece discs are usually marked.
3) Your dive shop is correct that the proper burst disc for a 3000 PSI cylinder is 5000 PSI.
4) Now that they've taken the burst disc out, you should not reuse it. Check out my post to A&I for photos of the $2000 of damage to my pickup truck caused by a reused burst disc
5) As long as you're replacing it you might as well put in a 5000 PSI one.
6) I don't fault the dive shop for following industry standards, but most sensible people would agree that it doesn't matter much whether you use a 5000 PSI or 5250 PSI burst disc.

 

[viperwsu]

I'll double check the number when I go pick it up today, but I have no illusions about not putting in a disk once it's been removed - that point has been hammered home in every thread I've read before starting this one. Fortunately, when I left the LDS last night they hadn't removed it - I hope that's still true, as Piranha says that it's not a standard size and isn't easily replaced.

If it is 5250 I'll agree that it's not meant for 3000 psi tanks, but they're saying it's meant for tanks with 4250 psi (or 5250) - they're reading the number on the disk as the service pressure, not the burst pressure.

 

[runsongas]

that is a head scratching decision from piranha though to have a non-standard size burst disc assembly on their valve

 

[JackD342]

I will have to check my stock at the shop over the weekend, but I do seem to recall that there are some burst disc assemblies that are marked with the Service Pressure rather than the burst pressure. But I also think the labeling includes the words Service Pressure and so is not open to interpretation. I guess a less experienced person that has only ever seen one type might not even think to ask/wonder if there is a different labeling convention.

 

[runsongas]

post a picture if you find one, i have only ever seen either burst pressure or both service and burst pressure marked.

 

[viperwsu]

that is a head scratching decision from piranha though to have a non-standard size burst disc assembly on their valve

I agree - here is the quote from the email Randy sent me regarding a conversation he had with the LDS before I even knew there was a problem (LDS contacted him):

"...I told him not to take it apart since the disks are a special size that is not available yet."

At the moment I'm not delving into that particular mire, but he also said he's sold "thousands" of these valves.

post a picture if you find one, i have only ever seen either burst pressure or both service and burst pressure marked.

I'll post one as soon as I get to the LDS after work.